One of the first items I ordered when I found out I was pregnant was the Organic Bamboo Belly Band from Baby-be-Mine. (I ordered it through Amazon.)
I cannot say enough good things about this product. At first, I used it to cover the fact that my jeans were un-buttoned, back when I could still get my pre-pregnancy jeans up over my hips. Now into the third trimester, I'm still using it! Now I use it to cover the not-so-lovely panel that maternity jeans are known for, when my shirt isn't quite long enough to cover it. It simply looks like I'm wearing a snug tank top or tube top underneath whatever I'm wearing.
I ordered 4 of these, one each in black, white, cocoa, and stone. The bamboo fabric is delightfully soft and easy to care for, requiring no special laundering. I've heard women complain of other types of belly bands being too short, or not staying up, but I've had no such problems with these.
After my daughter is born, I will continue to use them until I can button my old jeans again, and will also use them so that if I need to lift up my shirt to nurse, my saggy and stretch-marked post-baby belly and sides will be covered! And beyond that, hell, I'll probably just use them as regular ol' tube tops!